The German theologian Johann Maier von Eck (1486-1543) was a leading Roman Catholic opponent of Luther.

Johann Eck was born at Eck in Swabia, and like Martin Luther was of peasant stock. He studied at Heidelberg and other universities before becoming a doctor of theology in 1510. Eck taught at the University of Freiburg and after 1510 at the University of Ingolstadt. His academic career was early marked by a taste for humanist scholarship and intense criticism of ecclesiastical abuses, and he soon was widely known and respected as a scholar and orthodox churchman.

In 1517, when Luther, a professor of theology at the University of Wittenberg, published his 95 theses criticizing certain religious practices, Eck responded with a set of countertheses, which he called "Obelisks" and circulated privately. Karlstadt, a supporter of Luther's, obtained a copy of Eck's work and responded publicly with a collection of 400 theses. In 1518 Eck arranged for a debate with Luther and Karlstadt at Leipzig in the following year. At the debate Eck quickly disposed of Karlstadt and then took on Luther himself, skillfully drawing the reformer into extremely heretical positions and achieving a personal triumph.

When academic recognition was slow in coming, Eck took his case to Rome and elicited a papal bull from Leo X excommunicating Luther and condemning his position. Eck then brought the bull back to Germany and urged Emperor Charles V to apply force to Luther. Following Luther's condemnation, Eck remained the defender of Catholicism against him. Since Luther, however, refused to respond to his challenges, Eck turned his attention to other reformers and in a number of works condemned various theological errors. His career as the champion of orthodoxy culminated in his Confutation of the Protestant Augsburg Confession in 1530.

Because of his opposition to the Reformation, Eck has been criticized as a scholar and as a man, both by his contemporary opponents and by many historians since the 16th century. Although he was indeed given to excessive self-praise and could be extremely insulting to his enemies, he was a distinguished scholar, a practical administrator, and a man very much aware of and sympathetic to the various intellectual currents of his time.